At age 13, she is not "getting on."  Just like people, "seniors" can be
happy, healthy, and have many good years left.  My Holly is 12 and still
seems like a young cat.  My first cat lived to be almost 20.  That was many
years ago, and average lifespan for indoor cats has increased significantly
since then.

I'm sure you already know the real answer to your question...it's common
sense.  That is, you need to see a vet and it should be done ASAP.  There's
a good chance that this is something relatively simple, but it's always
better to catch problems early rather than wait until the problem may become
more difficult to treat.  You might even learn that it's a harmless skin
growth, but there is no way to make a diagnosis like that over the Internet
(and I am concerned over the fact that you said it seems to bother your cat
if you touch these growths).

MaryL